The invention relates to a method for cryptographically processing data, comprising feeding, to a cryptographic process, values, namely, the data and a key, and carrying out the process in order to form cryptographically processed data. Such method is generally known.
For cryptographically processing data, in practice there are often applied generally known processes. Examples of such cryptographic processes (algorithms) are DES and RSA [DES=Data Encryption Standard and RSA=Rivest, Shamir & Adleman], which are described, e.g., in the book “Applied Cryptography” by B. Schneier (2nd edition), New York, 1996.
Said processes are published since it was assumed that, in the event of sufficiently large key lengths, it would be impossible, on the basis of the processed data, to retrieve the original data and/or the key, even if the cryptographic process were known.
However, Cryptographic algorithms can be attacked—the goal always is to find the encryption key in use—in different ways: (1) Mathematical attacks like differential and linear cryptanalysis; (2) Hardware oriented attacks, called “Side Channel Attacks”, viz. attacks based on power consumption analysis or I/O timing analysis.
U.S. Pat. No. 5,745,577 discloses a method for advanced key scheduling of a secret key. The aim is to offer a protection against said mathematical attacks (differential and linear cryptanalysis) by mending the encryption algorithm. Amending the algorithm will cause change of its output and thus the disclosed method does not present any improvement against said “Side Channel Attacks”.